Dense hair causes you to be more vigilant when applying products, so you coat all of your strands. Other then that, it affects how you style (when I was younger and had really dense hair, I couldn't wear it in a single braid--it looked like a club.) Shouldn't really affect ingredient/product selection (maybe more hold?)

Copying and pasting so people might read it faster. Thanks Chloe. Gonna try this on wash day:

"How to Determine Hair Density

The density of your hair is simply how thin or thick it is. The number of hair follicles in a specific area of your hair, say a 1-inch area, determines your hair’s density.

The only way to truly determine density is to have someone literally examine a 1-inch square section of your scalp and count the number of hair follicles, or the number of hairs, in that 1-inch section. However, you can also do a simple hair density test with just two of your senses — vision and touch.

Kinky Hair

Kinky hair is hair that is very tightly curled. When you pull it straight out from the scalp, it immediately springs back as tight as it was before.

Make sure your hair is completely dry. Wet hair can feel and look thinner than it actually is.

Be sure that your hair has not been picked out, combed, or styled in any way.

Look closely at your hair from all angles, and see if you can see your scalp through the hair strands. If you can, your hair has very low density.

Curly and Wavy Hair

Curly hair is looser than kinky hair, but may still have quite a bit of tightness in it. Wavy hair is exactly what it sounds like. It has large or small waves, but little, if any, curliness or kinkiness.

Make sure your hair is hanging loosely. Do not part it; rather, let it fall into its natural shape.

Look at your hair from all angles. Can you see any scalp showing anywhere? If it very easily seen, your hair has low density.

Take your hair and gather it up as if you were going to put it in a ponytail. You may want to go ahead and secure it in a ponytail so that you won’t have to hold it. Brush it as smooth as you possibly can so that hair will not be “bunched up."

Examine your hair again from all angles. This time, if you see more scalp than when it was down, you can determine that your hair is of medium density. No scalp showing at all means your hair is of high density."